1. Field of the Invention
The present invention is concerned with photography, and more particularly, with the formation of color diffusion transfer images having whiter highlights.
2. Description of the Prior Art
A number of diffusion transfer photographic processes have been proposed wherein the resulting photograph comprises the developed silver halide emulsions retained with the dye image-carrying layer as part of a permanent laminate. The image-carrying layer is separated from the developed silver halide emulsions in said laminate by a light-reflecting layer, preferably a layer containing titanium dioxide. Illustrative of patents describing such products and processes are U.S. Pat. No. 2,983,606 issued Mar. 9, 1961 to Howard G. Rogers, U.S. Pat. Nos. 3,415,644; 3,415,645; and 3,415,646 issued Dec. 10, 1968 to Edwin H. Land, U.S. Pat. Nos. 3,594,164 and 3,594,165 issued July 20, 1971 to Howard G. Rogers, and U.S. Pat. No. 3,647,347 issued Mar. 7, 1972 to Edwin H. Land.
Referring more specifically to aforementioned U.S. Pat. No. 3,415,644, this patent discloses photographic products and processes employing dye developers wherein a photosensitive element and an image-receiving layer are maintained in fixed relationship prior to photoexposure and this fixed relationship is maintained after processing and image formation to provide a laminate including the processed silver halide emulsions and the image-receiving layer. Photoexposure is made through a transparent (support) element and application of a processing composition provides a layer of light-reflecting material to provide a white background for viewing the image and to mask the developed silver halide emulsions. The desired color transfer image is viewed through said transparent support against said white background.
In the utilization of unitary film structures such as these, it has been observed that color stain tends to build up in the image highlight areas in time. Perhaps the most commonly employed means for counteracting color stain in photographic products is the use of fluorescent dyes as optical brighteners. For example, U.S. Pat. No. 3,269,840 discloses a photographic material comprising a support carrying a baryta layer employing gelatin as the essential binder and having a water-soluble optical brightener and a water-soluble vinyl polymer incorporated therein. U.S. Pat. No. 3,743,531 discloses photographic material which includes a support, a substantially protein-free layer containing baryta, polyvinyl alcohol and an optical brightener carried on the support and optionally, a polymeric layer overcoated on the baryta layer. This photographic element additionally may include a blue pigment or a mixture of blue and magenta pigments in the baryta layer as a tint.
Though the use of certain binders for the baryta layer, such as polyvinyl alcohol, has improved the stability of the optical brightener to decomposition and loss of fluorescence, fluorescent dyes are subject to further disadvantages. Because they depend upon irradiation with ultraviolet light for emitting visible light, their efficiency is reduced when used in conjunction with conventional UV absorbers and their visual effectiveness differs according to the light, i.e., natural or artificial illumination used for viewing the photographic image.
One method of enhancing the whiteness of the non-image or highlight areas of color reflection prints without the use of fluorescent materials forms the subject matter of U.S. Pat. No. 3,802,881 issued Apr. 9, 1974 to Edwin H. Land and Stanley M. Bloom. As disclosed therein, a "non-fluorescent optical whitening reagent" is employed in association with the transfer image to balance the color stain, i.e., a non-fluorescent reagent which has a color complementary to that of the stain such that the combination of reagent color plus stain color reflects substantially white light. As discussed therein, the whitening reagent may be a pigment or a dye, and initially may be positioned in the processing composition or in a layer of the film unit provided that it does not absorb actinic radiation intended to expose the photosensitive strata and subsequent to processing, should be positioned in the light-reflecting layer and/or in a layer of layers of the image-receiving component.
The present invention also is concerned with the use of a non-fluorescent optical whitening reagent for enhancing the whiteness of the non-image areas of color reflection prints, but as used herein, the whitening reagent is initially positioned in the image-receiving component and is retained therein subsequent to processing.
Though U.S. Pat. No. 3,671,241 discloses the use of small quantities of a blue or purple dye in image-receiving elements employed in diffusion transfer processes, it is concerned with the formation of silver rather than color transfer images. The image-receiving layer employed in the subject patent does not contain a dye mordant as used in color diffusion transfer processes but comprises a stratum of a silver precipitating agent.